Wheelchairs typically have wheel axles, and hubs for mounting wheels thereto. Each hub may be mounted to a respective wheel axle end portion of a wheel axle. In particular, each hub may be arranged to receive a wheel axle end portion of a wheel axle. Each hub may therefore have a hub opening which is arranged to accommodate a wheel axle end portion.
In order to prevent relative rotation between the hub and the wheel axle, the wheel axle end portion may be provided with an axially protruding portion and the inner surface of the hub opening may be provided with a corresponding axial groove for receiving the axial protruding portion. To be able to mechanically withstand torque-related stress between the wheel axle and the hub during the operational lifetime of the wheelchair, there should be no more than a very small rotational play between the axial protruding portion and the axial groove. Mechanical strength withstand is especially of concern when the wheel axle is short, which is common in order to fulfil a desire for less wide wheelchairs. However, the play cannot be as small as would be desired, because that would render mounting of the hub to the wheel axle end portion difficult and would require that larger axial forces would have to be applied when fitting the hub around the wheel axle end portion. The application of large axial forces during assembly could cause damage to the wheelchair, especially in the case of a motorised wheelchair for which the wheel axle may be mechanically coupled to the gearbox of the wheelchair. Excessive axial forces during assembly could in particular cause damage to components inside the gearbox. The tolerances must thus be rather tight when constructing the hub and the wheel axle, which places high requirements on the manufacturing process.
A further aspect is that the small rotational play between the axial protrusion of the wheel axle end portion and the axial groove of the hub could affect the bolt with which the hub is fastened to the wheel axle. On one side of the wheelchair, i.e. at one specific wheel, the bolt could loosen, and on the opposite side wheel, the bolt could tighten. This may result in that the wheel could loosen, or even fall off completely.
Measures for preventing the loosening of the wheels may for example include higher quality bolts, locking washers, and bonding of the bolts with thread locks. It would however be desirable to simplify the hub and wheel axle design of a wheelchair and to further mitigate problems with previous solutions.